Climatic Change, Wars and Dynastic Cycles in China Over the Last Millennium
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CLIMATIC CHANGE, WARS AND DYNASTIC CYCLES IN CHINA OVER THE LAST MILLENNIUM DAVID D. ZHANG1,C.Y.JIM1, GEORGE C-S LIN1, YUAN-QING HE2, JAMES J. WANG1 and HARRY F. LEE1 1Department of Geography, University of Hong Kong, Pokfulam Road, Hong Kong E-mail: [email protected] 2CAREERI, Chinese Academy of Science, Lanzhou 730000, Gansu, China Abstract. In recent years, the phenomenon of global warming and its implications for the future of the human race have been intensively studied. In contrast, few quantitative studies have been attempted on the notable effects of past climatic changes upon human societies. This study explored the relationship between climatic change and war in China by comparing high-resolution paleo- climatic reconstructions with known war incidences in China in the last millennium. War frequencies showed a cyclic pattern that closely followed the global paleo-temperature changes. Strong and significant correlations were found between climatic change, war occurrence, harvest level, population size and dynastic transition. During cold phases, China suffered more often from frequent wars, population decline and dynastic changes. The quantitative analyses suggested that the reduction of thermal energy input during a cold phase would lower the land carrying capacity in the traditional agrarian society, and the population size, with significant accretions accrued in the previous warm phase, could not be sustained by the shrinking resource base. The stressed human-nature relationship generated a ‘push force’, leading to more frequent wars between states, regions and tribes, which could lead to the collapse of dynasties and collapses of human population size. War frequencies varied according to geographical locations (North, Central and South China) due to spatial variations in the physical environment and hence differential response to climatic change. Moreover, war occurrences demonstrated an obvious time lag after an episode of temperature fall, and the three geographical regions experienced different length of time lags. This research also shows that human population increases and collapses were correlated with the climatic phases and the social instabilities that were induced by climate changes during the last millennium. The findings proposed a new interpretation of human-nature relationship in the past, with implications for the impacts of anomalous global warming on future human conflicts. 1. Introduction The relationship between civilization and climatic change is of fundamental impor- tance, so much so that it can facilitate the rise or demise of culture (Cowie, 1998). It has been a long-standing belief that climatic change would lead to social, cultural and economic repercussions in human societies. For instance, Hsu (1998) advocated that micro-changes of temperature exerted notable influences on the fate of human civilization. Recently, important attempts have been made to use high-resolution paleo-climatic record to explain several pre-historical cultural breaks in certain time periods (deMenocal, 2001; Polyad and Asmerom, 2001; Weiss and Bradley, 2001; Wu and Liu, 2002). Extensive documentation has been made in attempts to Climatic Change (2006) 76: 459–477 DOI: 10.1007/s10584-005-9024-z c Springer 2006 460 DAVID D. ZHANG ET AL. assess the causes of wars (e.g., Pruitt and Snyder, 1969; Westing, 1988; Seabury and Codevilla, 1989; van Evera, 1999; Ge et al., 2002), but none tackled specifically the climatic change-war relationship. Webster’s (1975) study of pre-historical and early-historical societies suggested that warfare is an adaptive ecological choice under the conditions of population growth and resource limitation, although he did not obtain systematic scientific data to support his thesis. Malthus (1798) and many ecological studies considered that when a species (including human) population size exceeded a certain threshold that could not be supported by available resources, the population would crash. Such a collapse in human population, in Malthus’ view, was partially achieved by wars. The association between wars and the environ- ment has been recognized by some researchers (Ferguson, 1984; Stranks, 1997; Suhrke, 1997; Cowie, 1998). However, the existing literature tends to focus on the social and economic costs of current and future environmental changes. We believe that learning how past climatic changes had influenced human society is crucial to understanding the current human-nature situation and predicating the future. The last three decades witnessed intensive research on past climatic change around the world. The last 10 years work, in particular, has ushered significant improvements in high-resolution paleo-climatic reconstructions, using multi-proxy data networks to reconstruct past climate variations. A focus on the last millennium showed the global warming trend, from which it has been concluded that the last century was the warmest (Jones et al., 2001; Mann et al., 2003). It is reckoned that such refined paleo-climatic records could provide a strong basis to evaluate the intricate relationship between climatic change, wars and dynastic transitions. The large land area and geographical variations in China have permitted climate to express itself explicitly in its varied natural and cultural landscapes, and associ- ated modes of human occupancy and livelihood. The effect of climate has had the most far-reaching and persistent historical imprints on the country (Chang, 1946). In investigating the relationships of climate-war and climate-dynastic cycle, China would afford an excellent case study. In the course of China’s long history, volu- minous documentation in the palace archives of different dynasties, dating back to 880 BC, systematically recorded all major events. This valuable and comprehensive information repository provided a rich database for our study. We propose the hypothesis that long-term climatic change has brought sig- nificant shifts in land carrying capacity which could be considered as a variable in history. This view is contrary to the traditional one of Malthus, Darwin and many ecologists who hold land carrying capacity as a constant. Such capacity shifts could have influenced the well-being of the humankind socially, econom- ically and culturally not only in pre-historical time but also in recent history of agricultural societies. In favorable climatic phases, the land carrying capacity in- creased, the conflict for resources was reduced and the population grew fast. When climate became unfavorable, resulting in capacity decline, the population size with much accretions accumulated in the previous favorable period could not be sus- tained. Therefore, armed conflicts for limited resources largely increased in more CLIMATIC CHANGE, WARS AND DYNASTIC CYCLES 461 populated areas that could consequently lead to population crash and dynastic col- lapse. These perceived climate-war and climate-dynasty relationships have never been substantiated with scientific evidence. In this study, we adopted a new ap- proach to analyze quantitatively the climate-war and war-society relationships at the macro-scale, by comparing the paleo-climatic series with war, population and historical sequences. Through this high-resolution comparison, the degree of influ- ence extended by climatic change on wars and historical events may be examined and our hypothesis tested. 2. Data and Methods A group of researchers from the Nanjing Academy of Military Sciences has com- piled a multi-volume compendium that records exhaustively information on the wars that took place in China from 800 BC to AD 1911 (Editorial Committee of China’s Military History, 1985). The book includes an appendix with details of each war, including its inception year, participants, location, causes, and in most cases, the number of soldiers or combatants, casualties, proceedings and results. All of the 1672 wars listed in the authoritative treatise from AD 1000 to 1911 have been used as the database for this study. To avoid bias associated with different sources of information, only the reliable variables were used for scientific analysis, including year of inception, number, participants and location of the wars. Based on such information, the frequency, participant-type and geographical distribution of the wars can be calculated with reference to a time series. Some wars without reliable information on locations were put in an unidentified category. War classi- fication was based on the types of participants, particularly leaders of the two sides in the armed conflicts. The wars were grouped into rebellion and others (state and tribal wars). The times of dynastic changes were based on official records published by government bodies and historians. The dynasties included those that ruled most parts of China, and those established by remote tribes that once occupied an area equivalent to over 10 provinces of the current Chinese territory. The geographical occurrence of wars helped the assessment of climate-war as- sociation. According to the basic principles of physical regionalization of China (Ren et al., 1985; Zhao, 1986), China is divided into three macro regions for this study, namely: (1) North China with continental humid, semi-humid, semi-arid and arid temperate climate influenced by both the monsoons and the westerlies. Its average annual temperature ranges from very low to 14 ◦C. Major agriculture prod- ucts are spring wheat (northern part) and winter wheat (southern part). Economic activities are mainly pastoral because the relatively